Gas electrodes are well known in and for electrochemical operations. For their use, a gas is passed in contact with the electrode in the presence of a cooperating electrolyte. Most modern gas electrodes are highly porous and, either inherently or by purposive implementation, catalytically active. Quite importantly, the interior interstitial passageway wall surfaces within the electrode body should have good catalytic capability. Maximization of effective, available reaction-promoting surface area for given unit geometric volumes of the electrode configuration may thus be realized.
The indicated manner of electrode construction is advantageous for oxygen gas-bearing (or depolarized) electrodes, particularly cathodes, that are adapted for the electroreduction of oxygen in alkaline media.
Usage of such electrodes involves passage of the oxygen-bearing gas through the porous electrode body for contact with the involved electrolyte. Such practice is very desirable not only for electrolyzing functions but also for galvanic mode operations, as in fuel cells. Oxygen gas-bearing depolarized cathodes are particularly attractive for chlor-alkali and the like manufacturing cell operations.
A very good reason for employing oxygen gas-bearing porous electrodes to electrolyze common salt brine into chlorine and caustic, and for analogous production purposes, is economic. Significant savings in electrochemical power requirements for given workings are anticipatable due to substantial reductions achievable in needs for applied energy consumption when such electrodes are utilized.
Oxygen electrodes have often been catalyzed by various precious or semi-precious metals and compounds thereof. But, such noble metals as gold, osmium, palladium, platinum, silver, their alloys, oxides and other compositions and so forth are extremely expensive, especially for industrial applications. Thus, their consumption as catalysts for electrode preparation must be carefully controlled. Minimization of total quantity usage is usually done by deposition of precious catalyst materials in the form of thin plating or other layers over a suitable substrate, such as a porous nickel plaque.
It would obviously be desirable to have for ready usage an efficacious yet less costly way to provide satisfactory catalytically-active porous electrodes, especially for use in alkaline media as depolarized cathodes for electrolysis (or even for distinctive galvanic mode purposes).
Manganese oxide materials (including mixtures thereof) are known to be excellent electrocatalysts. These, in particular, include: various forms of manganese dioxide (MnO.sub.2); manganic or manganous oxide (Mn.sub.3 O.sub.4 -also known as "hausmannite"); and manganic sesquioxide (Mn.sub.2 O.sub.3). On reasonable evidence, it is fairly supposed that the Mn.sub.3 O.sub.4 form is likely the most chemically stable, especially in association with nickel, of the various indicated forms.
Many patent and literature references relate to the preparation and use, in diverse ways, forms and/or combinations, of electrodes involving manganese oxides or manganese peroxides (oftentimes in combination with other electrochemically active materials). These include: U.S. Pat. Nos. 1,296,188; 1,043,937; 1,143,828; 1,423,071; 1,510,172; 3,491,014; 3,535,217; 3,616,302; 3,627,669; 3,775,284; 3,915,837; and 3,948,684; Chemical Abstracts 7:3458; 42:5356c; 50:83b; 74:150359r; 76:62793e; 78:51823p; 79:142363a; 81:57517a; 81:20121r; 83:182053p; and 83:182059v; and Derwent 61865 S/39 and 10379 W/06 (all of which are herein incorporated by reference).
Despite the known art, reliable ways and means to effectively incorporate securely placed deposits of manganese oxide(s) in and for catalyzation of porous electrodes, and the associated desiderata, have heretofore been lacking and wanting; this being especially so in respect of very fine pore, large internal surface area electrodes of newer, modern type and style which are extremely difficult to efficiently internally catalyze when they are not inherently catalytic in nature.